Numpy Append To Array

I’m building a project for the Raspberry Pi that turns a relay on and off random times in a specific time window. To manage the time slots, I want to use a two-dimensional array

Solution 1:

np.append uses np.concatenate. It isn't a true copy of list append. It turns the new value into an array and does concatenate. But to do concatenate with structured arrays, all arrays have to have the same dtype (or at least compatible ones, hence the 'promotion' error.

This works:

In [4]: np.append(daily_slots, np.array((700, 800), dtype=daily_slots.dtype))
Out[4]: 
array([(  0, 1075970048), (700,        800)], 
      dtype=[('onTime', '<i4'), ('offTime', '<i4')])

This also works. I had to add the [] so that the 2nd array was 1d like the first. Without them it is 0d - in effect that's all that np.append adds to the game.

In [6]: np.concatenate((daily_slots, np.array([(700, 800)], dtype=daily_slots.dtype)))
Out[6]: 
array([(  0, 1075970048), (700,        800)], 
      dtype=[('onTime', '<i4'), ('offTime', '<i4')])

For growing and shrinking, a list is usually better. In this case a list of 2 element tuples, or may be a list of a custom class.

If it is a list of tuples, you could wrap it in np.array to turn it into a 2d array for ease of doing calculations.